I know things... A lot of things.
Join Date: Feb 2015
Motorcycle: GSXR 750 K4
Re: 2013 gsx-r 600 problems
So the idle was fine on the way home, but as soon as you put the pair blanking cap back on, it shot up to 4000rpm? I wonder if it was perhaps inadvertently tuned with the cap off, compensating for the fresh air leak with more fuel, so that it ended up rich after removing the leak. The reed valves in the PAIR ports would have to have been removed, for that to be possible, I believe. Have you tried removing the cap again, to see if the problem goes away when you do so?